It is intended to provide a compound useful as a GnRH receptor antagonist. The inventors further investigated propane-1,3-dione derivatives. As a result, they confirmed that a compound having a benzene ring or a thiophene ring substituted with a group represented by —SO2—R3 in a propane-1,3-dione derivative having 2-(1,3-dihydro-2H-benzimidazol-2-ylidene) has an excellent GnRH receptor antagonistic effect and accomplished the present invention. Because the compound of the present invention has a potent GnRH receptor antagonistic effect, it is useful for the treatment of sex hormone-dependent diseases, particularly GnRH-related diseases. Further, because the compound of the present invention has an excellent metabolic stability in human and few drug interactions, therefore it has preferable characteristics as a pharmaceutical used for the above-mentioned diseases.